AT&T is the third largest advertiser in the country and already yields big power in media circles. Its proposed merger with DirecTV will give it an even wider reach.

The merger will be closely watched by all types of ad-dependent media companies— TV networks and digital companies — as the telecom category spends a massive amount on advertising time and space. Last year, telecom was the third largest ad spending category in the U.S., behind retail and automotive, according to Kantar.